Fluid transport systems are well known and used in a number of applications. For example, heated fluids, such as melted chocolate, candy, or waxes, may be transported from one station to another during a manufacturing process. Other fluids, such as milk or beer, may be cooled and transported through conduits in a facility. Viscous materials, such as soap, lubricants, or food sauces, may require thermal treatment before being moved through a machine or facility.
One specific application of transporting a thermally treated fluid in a machine is the transportation of ink that has been melted from a solid ink stick in a phase change printer. Solid ink or phase change ink printers conventionally use ink in a solid form, either as pellets or as ink sticks of colored cyan, yellow, magenta and black ink, that are inserted into feed channels through openings to the channels. Each of the openings may be constructed to accept sticks of only one particular configuration. Constructing the feed channel openings in this manner helps reduce the risk of an ink stick having a particular characteristic being inserted into the wrong channel. Exemplary systems for delivering solid ink sticks in a phase change ink printer in this manner are well known.
After the ink sticks are fed into their corresponding feed channels, they are urged by gravity or a mechanical actuator to a heater assembly of the printer. The heater assembly includes a heater that converts electrical energy into heat and a melt plate. The melt plate is typically formed from aluminum or other lightweight material in the shape of a plate or an open sided funnel. The heater is proximate to the melt plate to heat the melt plate to a temperature that melts an ink stick coming into contact with the melt plate. The melt plate may be tilted with respect to the solid ink channel so that as the solid ink impinging on the melt plate changes phase, it is directed to drip into the reservoir for that color. The ink stored in the reservoir continues to be heated while awaiting subsequent use.
Each reservoir of colored, liquid ink may be fluidly coupled to a printhead through at least one manifold pathway. As used herein, liquid ink refers to solid ink that has been heated so it changes to a molten state or liquid ink that may benefit from being elevated above ambient temperature. The liquid ink is pulled from the reservoir as the printhead demands ink for jetting onto a receiving medium or image drum. The printhead elements, which are typically piezoelectric devices, receive the liquid ink and expel the ink onto an imaging surface as a controller selectively activates the elements with a driving voltage. Specifically, the liquid ink flows from the reservoirs through manifolds to be ejected from microscopic orifices by piezoelectric elements in the printhead. To provide differently colored inks to a printhead, each color of ink flows through a conduit, and the conduits may be grouped together into an ink umbilical assembly. As used herein “fluidly coupled to a printhead” refers to a fluid path being completed to a manifold, pressure chamber, or other receptacle for ink within a printhead prior to ejection of the ink from the printhead.
Typical prior art umbilical assemblies include one or more tubes arranged parallel to one another. For example, in a typical color printer four (4) tubes may be arranged in parallel, each carrying one ink of cyan, magenta, yellow, or black color. Some umbilical assemblies have more than one set of tubes leading to one or more printheads, for example, an eight tube umbilical could have two (2) tubes for each of the ink colors mentioned above. Many factors restrict the overall width of the ink umbilical, such as reservoir and printhead connections, routing requirements, space allocation, flexure for printhead travel, thermal efficiency in maintaining operation temperature, advantages in rapid warm up, and advantages with minimal system level molten ink volumes. Complementary to most of these objectives, the walls of each umbilical are typically relatively thin. The thin walls help conserve space, enhance flexibility, and allow more efficient heating of the ink in the tube so that it remains fluid or can be re-melted. Typical umbilical assemblies are extruded from silicone, which may be extruded into thin flexible tubes, which may also be extruded as a connected cluster of tubes or other side-by-side arrangements.
In some liquid inkjet printers, silicone umbilical tubes have been observed to allow ink components in the ink to seep through the tube wall. This seeping ink may be able to migrate to and enter an adjacent tube. In some cases, these migratory components may include ink dye. The dye may enter the adjacent tube in sufficient quantities to impact the quality of the colored ink carried in that tube. Consequently, image hues may shift as a result of the mixture of ink dyes within a conduit carrying ink to a printhead. The chemical compositions of certain colors of ink also affect migration, with some inks having a substantially higher rate of migration, while other colors have very little migration. Since silicone or other unintentionally permeable elastomers are common materials used in tubes carrying various types of fluid, particularly heated fluids, the problem of fluid migration could occur in other fields beyond printing where fluids are transported through tubes susceptible to migration. Descriptions herein of tube permeability are relative to the small molecular size of dye materials and potentially other fluid constituents. The tubes are not permeable in the more common term use as general leakage cannot occur. Chemical compatibility can be an issue between some fluids and elastomer type materials.
Proposed solutions for colored ink migration have disadvantages. One solution is to form the umbilical from a material that has little or no susceptibility to fluid migration, such as stainless steel or aluminum. While these materials effectively hinder ink dye migration, they lack the flexibility required for an umbilical that moves with a printhead on a carriage that traverses a printing media. Alternative elastomeric materials exhibit permeability to some degree, may be difficult to extrude into tubes having appropriate dimensions for a particular printer, and may become brittle over time when heated and cooled during the printer's operation. Other proposed solutions to ink migration may require tubes that are too thick to fit into the restricted spaces present in the printhead. An umbilical that mitigates the problems of fluid migration while also remaining thin and flexible benefits the fields of printing and fluid transportation systems. Additionally and critical to any valid solution, the umbilical must be cost effective and practical to fabricate and control thermally.